Enhanced Thermoelectric Performance of Zintl Phase Ca₉Zn_{4+ x}Sb₉ by Beneficial Disorder on the Selective Cationic Site

Zintl phase compounds Ca₉Zn_4+xSb₉ have promising thermoelectric properties due to their complex crystal structure and tunable interstitial Zn. In this work, we prepared nominal Ca₉Zn_4+xSb₉ (x = 0.5, 0.6, 0.7, and 0.8) using ball milling and hot pressing. Further decreased lattice thermal conductivity was obtained by isoelectronic substitution of Eu on the selective Ca site, which is farther away from the framework of [Zn_4+xSb₉]^δ- for the smaller disturbance of carrier transport. Together with the intensively enhanced carrier mobility, which is attributed to the decreased effective mass and the increased interstitial Zn by inclusion of Eu, an increased peak ZT value to &tild;1.05 at 773 K and an enhanced average ZT value to &tild;0.73 from 300 to 823 K were achieved in Ca_6.75Eu_2.25Zn_4.7Sb₉